The HK 4 pocket pistol was first introduced by Heckler & Koch in 1967 making it the first pistol produced by the company. Mass production of this pistol started in 1968 and continued until 1984. There were approximately thirty-eight thousand pistols produced during this time. Serial numbers 10001 to 36550 were for commercial distribution. Twelve thousand pistols were produced for the German police and other government agencies in the .32 ACP (7.65×17mm Browning SR) caliber with the designation P11 and were serial numbered 40001 to 52400.

It is thought that the basic design of the HK 4 is based on that of the Mauser HSc. The HK 4 was designated “4” because the pistol had the ability to be modular in four calibers. This means the frame and slide could accommodate three (3) different centerfire calibers by simply replacing the barrel/return spring assembly and inserting the proper magazine for the caliber of choice. The fourth caliber, .22 Long Rifle (.22 LR), requires the extractor faceplate and firing pin be moved to conform to the proper configuration for rimfire operation in addition to changing the barrel and magazine. The three centerfire calibers that the pistol can use are: .25 ACP (6.35×16mmSR); .32 ACP (7.65×17mm Browning SR); .380 ACP (9×17mm Short). Most standalone pistols were sold in .380 ACP and .32 ACP. All four calibers came as a two-box set with the extra barrels, magazines and a screw driver/cleaning kit in accompanying box. Read full description in Wikipedia

The HK 4 is a straight-blowback, double-action to single-action pistol. With a round in the chamber, a bullet may be fired by either pulling the trigger or by cocking the hammer and then pulling the trigger. The pistol automatically cocks the hammer after a round is fired. The safety incorporates a decocking mechanism that can safely decock the pistol with a round in the chamber. The hammer is decocked by putting the safety in the “safe” position and pulling the trigger, which allows the hammer to fall without striking the firing pin. When using center fire cartridges, there is a red marking on the top of the extractor that serves as a “chamber loaded” indicator. This feature has continued in current H&K pistols. The pistol incorporates a plastic buffer in the frame. The buffer, which is loosely installed in the frame, can be lost during cleaning or can wear out and needs to be replaced periodically.

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“The HK P9 is a semi-automatic pistol from Heckler & Koch in 9×19mm Parabellum and the first to use a variation of H&K’s roller delayed blowback system in a pistol format and polygonal rifling now common in H&K designs. Design began around 1965 and production ran between 1969 and 1978. Only 485 single-action P9’s were produced and were discontinued in 1970. A traditional double action version, the P9S (the S standing for Spannabzug, or “double-action trigger”) was manufactured in greater numbers.” read entire description here

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“The P7 is a German 9×19mm semi-automatic pistol designed by Helmut Weldle and produced by Heckler & Koch GmbH (H&K) of Oberndorf am Neckar. It was revealed to the public for the first time in 1976 as the PSP (Polizei-Selbstlade-Pistole—”police self-loading pistol”).”

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“The HK Mark 23 Caliber .45 ACP pistol gives shooters match grade accuracy equal to that of the finest custom made handguns — yet exceeds the most stringent operational requirements ever demanded of a combat handgun. The Mark 23 provides this accuracy without the need for hand-fitted parts common in custom-built match pistols costing thousands of dollars more. One of the most thoroughly tested handguns in history, the MK23/Mark 23 project originated in 1991 when HK began development for the U.S. Special Operations Command, the organization that directs the activities of America’s most elite military units, including the Navy SEALs and the Army Special Forces. On May 1, 1996, the first HK MK 23 pistols were delivered to the U.S. Special Operations Command for operational deployment, making the MK 23 the first caliber .45 ACP pistol to enter American military service since the venerable Government Model 1911A1. During testing, MK 23 pistols met the most stringent operational and accuracy requirements ever demanded of a combat handgun. Endurance testing demonstrated a service life of over 30,000 rounds of +P ammunition. To meet the reliability requirement, the pistol had to demonstrate a minimum of 2,000 mean rounds between stoppages (MRBS) with both M1911 ball and +P ammunition. All pistols exceeded the 2000 MRBS with an average of 6000 MRBS. In more than 450 accuracy test firings from a precision firing fixture at 25 meters, MK 23 pistols far exceeded the government requirement, averaging 1.44 inches, with 65 groups of less than one inch. There were four groups of .5 inches, with 5 rounds going through the same hole! The Mark 23 is available in .45 ACP”